Water is generally used as a fire extinguishing agent in fire extinguishing, and the water is discharged from a fire extinguishing vehicle towards a fire origin to lower the temperature of the fire origin or to reduce the amount of oxygen around the fire origin (that is, to perform smothering extinguishment).
Under such a situation that a fire extinguishing vehicle cannot approach a fire origin, for example, at the time of disaster or mountain fire, effective fire extinguishing work cannot be carried out from the ground.
To cope with this situation, a method of spraying water from above the fire origin using a helicopter or an aircraft on a water ship, is adopted.
In spraying water using the aircraft, a certain altitude should be kept from the viewpoint of ensuring safety of the aircraft against heat in the fire origin and an ascending air current.
However, water applied from the aircraft, when the distance from the fire origin is larger, is likely to be scattered in a wider area by an influence of an external force. Thus, water cannot be easily concentrated to the fire origin, and, further, is scattered as mist before the water arrives at the fire origin, making it impossible to effectively extinguish the fire.
In order to overcome this problem, a technique has been proposed in which the fire extinguishing agent is dropped in a gel form to reduce a scattering area of the fire extinguishing agent and to apply the whole amount of the used fire extinguishing agent for fire extinguishing (see Patent Literature 1).